Optimization of CR-39 as neutron dosimeter

The chemical etching parameters (etching time, temperature, normality of etchant etc.) for use of CR-39 as neutron dosimeter have been optimized. The CR-39 films placed in polyethylene radiator were exposed to 252Cf neutron source for different time intervals and the neutron fluences were varied from 4.68x106 to 2.7x108 n/cm2. Etched tracks were analyzed and counted at 400X with microscope and neutron recoil track density was calculated after every hour of etching. It was found that the track density increases up to a certain etching time and then decreases for higher etching time, which is considered due to removal of shallow tracks and overlapping of the tracks due to their size enlargement. Optimized etching conditions found are, 7 N NaOH solution at 70 deg C (±) for 9 hr with continuous stirring. However, we found a linear relationship between neutron fluence and track density. UV-visible spectra were also obtained and analyzed for the pristine and neutron irradiated CR-39 films in the wavelength range 200-700 nm at room temperature. As seen from absorption spectra, the absorption edge is shifted towards longer wavelength with increase of fluence and therefore, indicates a decrease in the band gap. The study may be important for the future high energy accelerators and Radioactive Ion Beam Facilities where CR-39 can be used as a neutron dosimeter. (author)